The present invention relates to a class of compounds having particular affinity for a specific cell surface receptor prevalent on certain cancer cells, e.g. lung carcinomas, malignant melanomas, gliomas, neuroblastomas, pheochromocytomas, colon carcinomas, renal carcinomas, breast carcinomas, prostate carcinomas and the like. In particular the present invention provides such compounds as agents for detecting and treating tumors, particularly tumors having cancer cells which possess a cell surface sigma receptor.
Lung carcinomas, malignant melanomas, gliomas, neuroblastomas, pheochromocytomas, colon, renal, prostate and breast carcinomas are aggressive forms of cancer, the early detection and treatment of which are of paramount importance. If left undetected or untreated for several years or even months the median survival time of patients having these types of cancers is dramatically reduced. of these cancers, lung cancer has lead to the highest number of fatalities. In 1992 alone, lung cancer caused about 165,000 deaths within the United States. Two major types of lung carcinomas are responsible for most of these deaths: small cell lung carcinomas (SCLC) and non-small cell lung carcinoma (NSCLC).
SCLC is a neuroendocrine tumor that secretes several peptide growth factors including bombesin/gastrin releasing peptide (BN/GRP). SCLC is responsive to chemotherapy and radiation therapy, but relapse occurs frequently, and the median survival time is only about one year.
NSCLC accounts for about 75% of all lung cancer cases and encompasses a variety carcinomas including adenocarcinomas, large cell carcinomas and squamous cell carcinomas. NSCLC tumors secrete transforming growth factor-alpha (TGF-xcex1) to stimulate cancer cell proliferation. NSCLC is generally treated with chemotherapy and surgical resection. However the median survival time for patients with NSCLC is only about 5 years.
Melanomas are among the most serious manifestations of skin cancer and lead to a greater number of fatalities than any other form of skin cancer. Melanomas can metastasize through the lymphatic system to regional nodes and then via the blood to secondary sites on the skin or in the liver, lungs and brain. Whereas the prognosis for superficial spreading melanomas can be quite good, there is a much poorer prognosis for nodular melanomas in which distant metastases frequently form.
Breast cancer is a major cause of death for women, and estrogen receptors ave been reported to play a major role in the development and growth of breast tumors. Deprivation of estrogen is one of the clinically effective methods for the treatment of breast cancer patients. Several growth factors such as insulin-like growth factor I (IGF-I), transforming growth factors (TGF-xcex1 and -xcex2), epidermal growth factor (EGF), and platelet-derived growth factors have been shown to be involved in the growth and progression of human breast cancer cells. Some growth factors such as TGF-xcex2 act as inhibitors of tumor growth. Despite the development of numerous antiestrogen and other drugs, the clinical utility of antiestrogen is limited due to resistance by the tumor cells.
Many lives could be saved if lung carcinomas, melanomas, gliomas, neuroblastomas, pheochromocytomas, colon, prostate and renal carcinomas and breast tumors were detected and treated at an early stage. Moreover many patients are reluctant to undergo radical surgical or broad spectrum chemotherapy procedures which are frequently used to treat such cancers since these procedures can cause disfiguration or disablement.
Current techniques diagnose breast cancer by first identifying suspect tumors by single plane or 2D mammography screening. A biopsy is then required to differentiate tumors from other lesions. In the United States alone, 21 million mammographies are performed each year; 700,000 suspect tumors are biopsied and 182,000 women are diagnosed with breast cancer. This suggests that 400,000-500,000 women are subject to unnecessary biopsy each year.
Accordingly an outstanding need exists for highly selective and non-invasive procedures permitting early detection and treatment of cancer.
A variety of radiopharmaceuticals have been evaluated for diagnostic imaging. For example, Michelot, J. M. et al. (1991 J. Nucl. Med. 32:1573-1580; Meyniel G. et al. (1990 C.R. Acad. Sci. Paris 311(1):13-18; and French Patent Publication No. 2,642,972 by Morean et al. have disclose [123I and 125I]N-(diethylaminoethyl)4-iodobenzamide (i.e. IDAB) for imaging malionant melanoma in humans. Unfortunately, the synthesis of IDAB is problematic and, more significantly, IDAB is taken up in high concentrations by non-melanoma cells in the liver and lung. Accordingly, IDAB does not have optimal specificity for melanoma cells and its uptake by non-tumor cells undermines its utility for routine screening of cancer.
U.S. Pat. No. 4,279,887 to Baldwin et al., U.S. Pat. No. 5,154,913 to De Paulis et al. and Murphy et al. (1990 J. Med. Chem. 33:171-178) disclose radioiodonated benzamide compounds for use in imaging the brain only, e.g. 123I-N-xcex2-phenethyl-o-iodobenzamide or (S)-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-hydroxy-3-iodo-6-methoxybenzamide (IBZM). However, the structure and utility of the compounds disclosed by Baldwin et al., De Paulis et al. and Murphy et al. is distinct from those provide herein.
The present invention provides compounds which bind with high specificity and affinity to the cell surface of cancer cells. These compounds bind, for example, to receptors on the cancer cell surface. One such receptor is a sigma receptor. Sigma receptors are known to be present on neural tissues and certain immortalized neuroblastoma and glioma cell lines (Walker et al. 1990 Pharmacol. Reviews 42: 355-400; and Villner et al. 1992 in Multiple Sigma and PCP Receptor Ligands: Mechanisms for Neuromodulation and Neuroprotection? Kamenka et al., eds. NPP Books, pp 341-353). However, it has been surprisingly found by the present inventors that sigma receptors are prevalent on some types of cancer cells, e.g. neuroblastoma, melanoma, glioma, pheochromocytoma, colon, renal and lung carcinoma cells. Recently, John et al. have found that MCF-7 breast tumor cells express sigma receptors. (1994 J. Med. Chem. 37: 1737-1739). Therefore the compounds of the present invention are useful for detecting and treating tumors, e.g. those containing cells with sigma receptors.
The present compounds are also useful for diagnostic imaging any tissue having a sigma receptor, e.g., a neural tissue such as the brain or spinal cord.
The present invention provides a method for diagnosing a mammal for the presence of a mammalian tumor which includes administering to a mammal a diagnostic imaging amount of a compound of the present invention, and detecting binding of the compound to a tumor in the mammal. The compounds of the present invention are of the general formula I. 
wherein:
X is a radionuclide;
Z is xe2x95x90O or two xe2x80x94H;
each R1 is independently H, halo, lower alkyl or lower alkoxy;
Ra and Rb are independently H, halo, lower alkyl, lower alkoxy or Ra and Rb together with the carbon atoms to which they are attached form a cycloalkenyl or heterocyclic ring;
R2 is xe2x80x94N(R3)2 or a 5 to 7 membered nitrogen containing heterocyclic ring which is unsubstituted or substituted with at least one alkyl or substituted or unsubstituted arylalkyl substituent;
each R3 is independently hydrogen or lower alkyl;
j and y each are independently an integer from 0 to 6;
q is an integer from 0 to 2; and with the proviso that the compound is not an iodine radioisotope of (N-diethylaminoethyl)-4-iodobenzamide.
The present invention also provides a method for treating a mammalian tumor which includes administering to a mammal a composition including a tumor-inhibiting amount of a compound of formula I.
The present invention further provides a method for diagnostic imaging of a mammalian tissue which has cell surface sigma receptors which includes administering to a mammal a diagnostic imaging amount of a compound of the present invention and detecting an image of a tissue having an abundance of cells with sigma receptors.
A further aspect of the present invention provides a method for in vitro detection of a cancer cell in a mammalian tissue sample which includes contacting a mammalian tissue sample with an in vitro diagnostic imaging amount of a compound of formula I for a time and under conditions sufficient for binding of the compound to the cancer cell and detecting such binding.
Another aspect of the present invention provides preferred compound of formula I, e.g. a compound of any one of formulae II, III or IV. 
wherein Z, Ra, Rb, R1, q, j are as described above;
Q is a radionuclide, halide or an activating group;
R4 is xe2x80x94N(R3)2 or an N-linked 5 to 7 membered nitrogen containing heterocyclic ring which can have at least one alkyl or substituted or unsubstituted arylalkyl substituent, wherein each R3 is independently lower alkyl or hydrogen;
R5 is a 5 to 7 membered nitrogen containing heterocyclic ring which can have at least one alkyl or substituted or unsubstituted arylalkyl substituent;
m is an integer from 0 to 6;
n is an integer from 3 to 6. Such preferred compounds can also be used in the method of the present invention.